The present invention relates to a semiconductor device and a method of fabricating the same, and more particularly to a semiconductor device in which an insulating film having a low relative dielectric constant is used as an interlayer insulating film of a multi-layer interconnection structure, and a method of fabricating the same.
In recent years, semiconductor integrated circuits have kept on promoting high integration, and as circuits have been shrunk, a request for a wiring resistance and a capacity of an interlayer insulating film has become severe from a viewpoint of a processing speed and power consumption of the semiconductor devices. In view of this actual situation, a metal such as copper having a small resistance has been used as a wiring material, or an insulating film such as methyl siloxane having a low relative dielectric constant has been used as an interlayer insulating film, thereby forming multi-layer interconnection.
At present, a damascene method as a buried copper wiring technique is used in patterning of a copper wiring which has been conventionally difficult to pattern in many cases.
On the other hand, an organic insulating film such as a methyl siloxane film having a low relative dielectric constant of 3.0 or less has been used as an insulating film, and a technique for applying such an organic insulating film to the multi-layer interconnection has been developed.
However, although the insulating film having a low relative dielectric constant is required, the insulating film having a relative dielectric constant of 3.0 or less has low resistance against a damage caused during the etching, and also has low mechanical strength. As a result, various adverse effects are encountered when this sort of insulating film is used as an interlayer insulating film of the copper multi-layer interconnection which is formed by utilizing the damascene method.
In the case of the insulating film having the low relative dielectric constant, while the etching is performed, a methyl group of a surface layer is easy to de-couple and thus a molecular structure is easy to destroy. As a result, the insulating film is damaged, so that a layer having a reduced carbon concentration (hereinafter referred to as “a damaged layer”) is formed. Water is absorbed on the damaged layer having the de-coupled methyl group. When a heat treatment in a wiring material-burying process after etching or a subsequent upper layer interconnection structure-forming process is performed, the water absorbed on the damaged layer oxidizes a barrier metal, of which a sidewall for a via hole is made, in the vicinity of the damaged layer to degrade adhesiveness between a wiring material and the barrier metal, thereby causing deterioration of electrical characteristics of the semiconductor device and degradation of reliability thereof.
Japanese Patent KOKAI No. 2002-353308 has reported a technique with which the damaged layer formed in such a manner is exposed to hexa methyl disilazane (HMDS) gas ambient atmosphere or HMDS liquid is applied to the damaged layer to re-bond a hydrocarbon group such as a methyl group to a portion having a de-coupled methyl group, thereby repairing that portion to its former state.
However, as the relative dielectric constant becomes lower, an amount of damage received by the film further increases, and thus it is feared that the film is more largely damaged than it can be perfectly repaired. As a result, the technique disclosed in Japanese Patent KOKAI No. 2002-353308 involves such a defect that it is impossible to employ an insulating film having too low relative dielectric constant. Thus, a method disclosed in Japanese Patent KOKAI No. 2002-353308 employs an insulating film having a relative dielectric constant of about 2.7.
On the other hand, United States Patent Application Publication No. 2002/0187625 has reported the following technique as one of methods of, when an insulating film having a low relative dielectric constant is used in multi-layer interconnection, suppressing a damage caused by etching. That is to say, with this technique, after a wiring is formed in an insulating film which has a relatively high relative dielectric constant and which has high etching resistance, this insulating film is etched away by etching, and an insulating film having a low relative dielectric constant is newly buried in the etched portion.
However, in this technique, when the insulating film having the relatively high relative dielectric constant is removed by the etching after formation of the wiring, its portion under the wiring cannot be perfectly removed to be partially left. For this reason, although the insulating film having the low relative dielectric constant can be buried in the portion from which the insulating film having the relatively high relative dielectric constant could be removed by the etching, the insulating film having the relatively high relative dielectric constant is left to the last in the portion from which the insulating film having the relatively high relative dielectric constant could not be perfectly removed by the etching.